Dehumidifying air handling unit and desiccant wheel therefor

ABSTRACT

A dehumidifying air handling unit for an HVACR system includes a housing, a desiccant wheel, and a cooling heat exchanger. A main airflow path extending through the housing from an air inlet to and air discharged outlet of the housing. The desiccant wheel includes a first end and a second end that are each disposed in the main airflow path and a metal organic framework desiccant that is moved between the first end and the second end. A desiccant wheel includes a metal organic framework desiccant disposed on a surface of the desiccant wheel. Rotation of the desiccant wheel moves a position of the surface between a first end and a second end of the desiccant wheel. The metal organic framework desiccant has an majority absorption-desorption operating band of 25% relative humidity or less.

FIELD

This disclosure relates generally to a heating, ventilation, airconditioning, and refrigeration (“HVACR”) systems. More specifically,this disclosure relates to a dehumidifier air handling unit (“AHU”) usedin HVACR systems.

BACKGROUND

HVACR systems are generally used to heat, cool, and/or ventilate anenclosed space (e.g., an interior space of a commercial building or aresidential building, an interior space of a refrigerated transportunit, or the like). An AHU is part of a HVACR system that is used toregulate and circulate air. A ductwork ventilation system can beconnected to the AHU and directs conditioned air from the AHU to theenclosed space and air from the conditioned space to the AHU. The AHUcan include a housing, fan(s), and a heat exchanger(s). The AHU can be adehumidifying AHU that includes a desiccant wheel for dehumidifying air.

BRIEF SUMMARY

A heating, ventilation, air conditioning, and refrigeration (“HVACR”)system can be utilized to heat and/or cool a conditioned space. TheHVACR system can utilize an air handling unit (“AHU”) to regulate andcirculate air. The air handling unit receives air (e.g., air from theconditioned space, ambient air, and the like) and discharges conditionedair (e.g., heated, cooled, dehumidified, filtered, and the like) that issupplied to the conditioned space. The air handling unit can be adehumidifying air handling unit in which the conditioning of the airincludes dehumidification.

In an embodiment, a dehumidifying air handling unit for an HVACR systemincludes a housing, a desiccant wheel, and a cooling heat exchanger. Thehousing includes an air inlet and an air discharge outlet. A mainairflow path extends through the housing from the air inlet to the airdischarge outlet. The desiccant wheel includes a first end disposed inthe main airflow path, a second end disposed in the main airflow pathdownstream of the first end, and a metal organic framework (“MOF”)desiccant. The desiccant wheel is configured to rotate to move the MOFdesiccant between the first end and the second end of the desiccantwheel. The cooling heat exchanger is disposed in the main flow pathdownstream of the first end of the desiccant wheel and upstream of thesecond end of the desiccant wheel. The MOF desiccant has an majorityabsorption-desorption operating band of 25% relative humidity or less.

In an embodiment, a desiccant wheel is configured to be rotated withinan air exchange unit of an HVACR system. The desiccant wheel includes afirst end, a second end, and a MOF desiccant. The MOF desiccant isdisposed on a surface of the desiccant wheel. Rotation of the desiccantwheel moves a position of the surface between the first end and thesecond end. The MOF desiccant has an majority absorption-desorptionoperating band of 25% relative humidity or less.

BRIEF DESCRIPTION OF THE DRAWINGS

Both described and other features, aspects, and advantages of an airhandling unit and desiccant wheel will be better understood with thefollowing drawings:

FIG. 1 is a schematic diagram of an embodiment of an HVACR system thatincludes an air handling unit with a desiccant wheel.

FIG. 2A is a partial schematic front view of channels in an embodimentof a desiccant wheel.

FIG. 2B is a cross-section of one of the channels of the desiccant wheelin FIG. 2A, according to an embodiment

FIG. 3 is a graph of isotherms for an embodiment of an MOF desiccant fora desiccant wheel.

FIG. 4 is a graph of isotherms for another embodiment of an MOFdesiccant for a desiccant wheel.

Like references in the drawings refer to like features.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an embodiment of a heating,ventilation, air conditioning, and refrigeration (“HVACR”) system 1. TheHVACR system 1 is configured to condition (e.g., heat, cool, dehumidify,and the like) a conditioned space 3 by supplying conditioned air to theconditioned space 3. The HVACR system can include a ductwork ventilationsystem 5 and an air handling unit (“AHU”) 10. The AHU 10 is configuredto provide conditioned air that conditions the conditioned space 3. Forexample, the AHU 10 is configured to discharge conditioned air at aparticular temperature (e.g., at a predetermined temperature, within apredetermined temperature range, or the like) and at a particularhumidity (e.g., at a predetermined humidity, within a predeterminedhumidity range, at a particular relative humidity, within apredetermined relative humidity range, or the like). For example, theparticular temperature and humidity for the discharged conditioned airmay be based on a difference(s) between a current temperature and/or acurrent humidity of the conditioned space 3 and a desired temperatureand/or a desired humidity for the conditioned space 3.

The AHU 10 is connected to the conditioned space 3 by a ductworkventilation system 5. Conditioned air discharged from the AHU 10 isdirected to the conditioned space 3 through the ductwork ventilationsystem 5. The ductwork ventilation system 5 configured to distribute theconditioned air discharged from the AHU 10 to the conditioned space 3.

The AHU 10 includes a housing 12 with an air discharge outlet 14 and anair inlet 16. Air enters the AHU 10 through the air inlet 16, isconditioned as it flows through the AHU 10, and the conditioned air isdischarged from the air discharge outlet 14. The AHU 10 conditions theair as it flows through the housing 12 from the air inlet 16 to the airdischarge outlet 14. The conditioned air flows from the air dischargeoutlet 14 into the conditioned space 3. As shown in FIG. 1 , theductwork ventilation system 5 can be respectively connected to the airinlet 16 and the air discharge outlet 14 of the AHU 10. In anembodiment, the HVACR system 1 may include one or more air filters (notshown). The air filter(s) may be located within the AHU 10 and/or theductwork ventilation system 5. For example, an air filter may be locatedwithin the housing 12 near the air inlet 16.

Air enters the AHU 10 through the air inlet 16. The air entering the airhandling unit includes a flow of return air F_(R) from the conditionedspace 3 and a flow of ambient air F_(A) (e.g., air from the externalenvironment, outdoor air, the like). As shown in FIG. 1 , the air inlet16 can include a first air inlet 16A and a second air inlet 16B. Forexample, the air inlet 16 can be an air inlet section of the AHU 10 thatincludes the air inlets 16A, 16B of the AHU 10. The first air inlet 16Ais a return air inlet which is fluidly connected to the conditionedspace 3. Return air F_(R) from the conditioned space 3 flows into thehousing 12 of AHU 10 through the first air inlet 16A. For example, theductwork ventilation system 5 is connected to the first air inlet 16A.In an embodiment, the second air inlet 16B is an opening, vent, or inletof the housing 12 that is fluidly connected to the ambient outsideenvironment (e.g., the outside of a building, the external outdoorenvironment, and the like). Ambient air F_(A) flows into the AHU 10through the second air inlet 16B.

The AHU 10 includes a cooling heat exchanger 30 and a desiccant wheel 40that are disposed within the housing 12. The air flows through thedesiccant wheel 40 and the cooling heat exchanger 30 as the air flowsfrom the air inlet 16 to the air discharge outlet 14 within the housing12. The AHU 10 can also include one or more fan(s) 80 that blow anddirect air through the housing 12. As shown in FIG. 1 , a fan 80 can bedisposed within the housing 12.

In an embodiment, the AHU 10 has a cooling mode. In the cooling mode,air enters the housing 12 of the AHU, is cooled and dehumidified withinthe AHU 10, and the cooled and dehumidified air is then discharged fromthe housing 12 and to conditioned space 3. In the cooling mode, the heatexchanger 30 is a cooling heat exchanger which cools the air and thedesiccant wheel 40 dehumidifies the air. In an embodiment, the AHU 10may include a heater 65 (e.g., an electric heater, a combustion heater,or the like) for heating the air before it passes through the desiccantwheel 40. The heater 65 disposed upstream of the first end 46A of thedesiccant wheel 40. The heater 65 can be used to improve theeffectiveness of the desorption of the water from the desiccant into theair. Relative to previous desiccants, the desiccant in the desiccantwheel 40 at least reduces the amount of heating provided by the heater65 relative to conventional desiccants. This can advantageously reducethe amount of power utilized by the AHU 10 and the HVACR system 1 tocondition the conditioned space 3. In some embodiment, the desiccant isable to provide the dehumidifying without the heater 65. The desiccantin the desiccant wheel 40 is

In an embodiment, the AHU 10 has a heating mode that heats the airflowing through the AHU 10. In an embodiment, the AHU may be configuredto operate the heat exchanger 30 as a heat pump to heat the air as itpasses through/along the heat exchanger 30. In an embodiment, the AHU 10may also include a heater 60 (e.g., an electric heater, a combustionheater, or the like) for heating the air in a heating mode. The heatercan be disposed downstream of the first end 46A of the desiccant wheel40.

In an embodiment, the AHU 10 may have a no air recycle configuration inwhich the AHU 10 does not utilize any return air F_(R) (e.g., the AHU 10utilizes 100% ambient air F_(A)). The no air recycle configuration maybe utilized by the AHU 10 in any one of its various modes (e.g., heatingmode, cooling mode, and the like). For example, the no air recycleconfiguration may block the first air inlet 16A for the return airF_(R). In such an embodiment, the AHU 10 may include an air-to-air heatexchanger (not shown) and/or a cooler (not shown) (e.g., a cooling heatexchanger) disposed between the second air inlet 16B and the first end46A of the desiccant wheel 40. In an embodiment, the air-to-air heatexchanger and the cooler can be disposed upstream of the heater 65. Theair-to-air heat exchanger has a first pathway and a fluidly separatesecond pathway in a heat exchange relationship (e.g., a shell sidepathway and a tube side pathway, or the like). The air flows from thesecond inlet 16A through the first pathway of the heat exchanger,through the cooler, then through the second pathway of the heatexchanger.

The AHU 10 has a main airflow path 18 that extends through the housing12 from the air inlet 16 to the air discharge outlet 14. Air enteringthe AHU 18 (e.g., the return air F_(R) and the ambient air F_(A) whichare to be conditioned) flows from the air inlet 16 to the air dischargeoutlet 14 by traveling through the main airflow path 18. In anembodiment for a cooling mode, the air is dehumidified and cooled as itflows through the main airflow path 18.

The main airflow path 18 includes a plurality of airflow sections. Inparticular, the main airflow path 18 includes a first airflow section20A, a second airflow section 20B, and a third airflow section 20C. Thefirst, second, and third airflow sections 20A, 20B, 20C are arranged inthat order within the main airflow path 18. With respect to the flow ofair through the main airflow path 18 (e.g., the air flowing from the airinlet 16 to the air discharge outlet 14): the second airflow section 20Band third airflow section 20C are each downstream of the first airflowsection 20A, and the third airflow section 20C is downstream of thesecond airflow section 20B. The second airflow section 20B is disposedbetween the first airflow section 20A and the third airflow section 20Calong and within the main airflow path 18. The air flows from the airinlet 16 into the first air flow section 20A. The air then flows fromthe first airflow section 20A to the second airflow section 20C. The airthen flows from the second airflow section 20B to the third airflowsection 20C. The air then flows from the third airflow section 20C tothe air discharge outlet 14

The desiccant wheel 40 is rotatable within the housing 12. The AHU 10includes a motor 44 configured to rotate the desiccant wheel 40 relativeto the housing 12. The desiccant wheel 40 can be supported on a shaft42. In an embodiment, the desiccant wheel can have a wheel shape. Thegeneral shapes and rotation for a desiccant wheel within an HVACR systemis generally known within the art. For example, the shaft 42 extendingthrough the desiccant wheel 40 at or near its center point. In anembodiment, the desiccant wheel 40 may be affixed to the shaft 42, andthe motor 44 is configured to rotate the shaft 42. In anotherembodiment, the desiccant wheel 40 may be configured to be rotatablesupported on the shaft 42, and the motor 44 may be configured to apply aforce that rotates the desiccant wheel 40 on the shaft 42. For example,the motor 44 can rotate a roller, gear, or the like, that is in contactwith a circumferential surface of the desiccant wheel 40.

During operation, the desiccant wheel 40 rotates within the firstairflow section 20A and the third airflow section 20C. The desiccantwheel 40 has a first end 46A and a second end 46B that are oppositeends, with respect to the airflow sections 20A and 20C. The first end46A and the second end 46B are opposite each other along the diameter ofthe desiccant wheel 40. The first end 46A is disposed in the firstairflow section 20A and the second end 46B is disposed in the thirdairflow section 20C. The desiccant wheel 40 has a plurality of sectors.For example, a sector generally has a wedge shape. As the desiccantwheel 40 rotates, each sector is recurrently moved from being in thefirst airflow section 20A to being in the third airflow section 20C andthen back to being in the first airflow section 20A.

As it rotates, the desiccant wheel 40 adsorbs moisture from the air inthe third airflow section 20C, and releases moisture into the air in thefirst airflow section 20A. The moisture adsorbed by the desiccant whiledisposed in the third airflow section 20C is de-adsorbed/released intothe air flowing through the first airflow section 20A.

The heat exchanger 30 is disposed in the second airflow section 20B. Theair flows across the heat exchanger 30 (e.g., through channels in thecooling heat exchanger 30, along outer tube surfaces of the cooling heatexchanger 30, and the like) as the air flows through the second airflowsection 20B. In an embodiment, the heat exchanger 30 adsorbs heat fromthe air and cools the air as the air flows across the heat exchanger 30.A colder fluid F_(CF) separately flows through the heat exchanger 30 andadsorbs heat from the air flows across the heat exchanger 30. In anembodiment, the colder fluid F_(CF) can be, for example but not limitedto, a chiller fluid, an expanded refrigerant, and the like. The heatexchanger 30 may be an evaporator in a refrigerant circuit. In anembodiment, the heater 65 and/or the heater 60 may be a condenser forthe refrigerant circuit that includes the heat exchanger 30 as anevaporator or for in a refrigerant circuit used to cool the colder fluidF_(CF).

As discussed above the AHU 10 conditions air F₁ that is a mixture ofreturn air F_(R) and ambient air F_(A). The ambient air F_(A) generallyhas higher moisture content than the return air F_(R). The temperatureand relative humidity of the ambient air F_(A) can vary depending upon,for example, the geographic location, season, and current weather at thelocation in which the HVACR system 1 is being employed. The ambient airF_(A) has a significantly higher moisture content in more humid climates(e.g., locations closer to the equator, locations near the ocean, islandlocations, and the like). The AHU 10 may be utilized to dehumidify, forexample, ambient air F_(A) with a temperature of at or about 20° C. toat or about 40° C. and a relative humidity (“RH”) that is from at orabout 30% to at or about 80%. For example, the ambient air F_(A) can be˜32° C. and ˜55% relative humidity (“RH”).

The air flowing through the third airflow section 20C is at a lowertemperature than the air flowing through the first airflow section 20A.The temperature difference increases the relative humidity of the air.The cooled air flowing into the third airflow section 20C has a higherrelative humidity. In an embodiment, the cooled air flowing into thethird airflow section 20C from the second section 20B has a relativehumidity that is about 80% or greater.

The desiccant wheel 40 includes channels 48 that extend through thethickness of the desiccant wheel 40. The air flows through the desiccantwheel 40 by flowing through its channels 48. The desiccant wheel 40includes a large number of the channels 48. For example, the desiccantwheel 40 can include at least one hundred of the channels 48. In someembodiment, a desiccant wheel 40 can includes thousands (i.e., at leasta thousand) of the channels 48. The channels 48 rotate along with therotation of the desiccant wheel 40. For example, the rotation causes achannel 48 to recurrently from disposed in the first airflow section20A, to disposed in the third airflow section 20C, and then disposedback in the first airflow section 20A.

The desiccant wheel 40 includes a desiccant. The desiccant is coated onthe surfaces/sides of the channels 48. The air flows across thedesiccant as it flows through the channels 48 of the desiccant wheel 40.The coating of the desiccant is discussed in more detail below. Thedesiccant is configured to switch between adsorbing water and desorbingwater as the desiccant is rotated on desiccant wheel 40. The exposure ofthe desiccant on the desiccant wheel 40 to a flow of air causes waterdesorption into the air (e.g., the air to hold water from the desiccant)can also be referred to as regenerating the desiccant. The properties ofthe desiccant are described in more detail below.

As it flows along the main air flow path 46A, the air flows through thefirst end 46A of the desiccant wheel 40, then along the cooling heatexchanger 30, and then flows through the second end 46B of the desiccantwheel 40. The air F₁ flowing into the first airflow section 20A has arelative humidity of at least ˜50% and is at a temperature of at least25° C. In an embodiment, the air F₁ flowing in the first airflow section20A has a relative humidity RH₁ from ˜50% to ˜75% and a temperature T₁from ˜25° C. to ˜27° C.

In an embodiment, the air is cooled as it flows over/through the heatexchanger 30 in the second airflow section 20B. Some of the moisture inthe air may condense as the air flows past/through the heat exchanger30. The condensed moisture can flow into a drip tray of the heatexchanger 30. The cooled air F₃ flowing from the second airflow section20B and into the third airflow section 20C can have a temperature T₃from ˜10° C. to ˜14° C. and a relative humidity RH₃ from ˜80% to ˜95%.

The air then flows over/through the second end 46B of the desiccantwheel 40. The desiccant in the second end 46A adsorbs moisture from theair as it flows through the third airflow section 20C. The dehumidifiedair F₄ after flowing over/through the second end 46B of the desiccantwheel 40 has a temperature T₄ from ˜14° C. to ˜19° C. and a relativehumidity RH₃ of ˜65%. The air then flows to the air discharge outlet 14.The conditioned air FD discharged from the AHU 10 can have can have atemperature T_(D) from of 14-19° C. and a relative humidity T_(D) of 65%or less. The desiccant wheel 40 includes a metal-organic framework(“MOF”) desiccant. A MOF desiccant includes metal ions, and/or clustersof metal ions, bound together with an organic linker. In an embodiment,the organic linker can be a ligand. In an embodiment, the MOF desiccantis applied in the form of a coating applied to at least one surface ofthe desiccant wheel 40. As shown in FIG. 1 , the desiccant wheel 40 caninclude a frame 50 and the coating can be applied to the frame 50 of thedesiccant wheel 40. For example, the coating applied to the channels 48formed in the frame 50 of the desiccant wheel 40. The coating is adesiccant composition that includes the MOF desiccant and a binder. Inan embodiment, the surface is a metal surface of the desiccant wheel 40.

FIG. 2A is a partial schematic front view of a plurality of the channels48 in the desiccant wheel 40, according to an embodiment. The channels48 extending into the page in FIG. 2A The frame 40 includes a pluralityof substrates 49A, 49B that form the channels 48. For example, a flutedsubstrate 49B can be stacked between a pair of flat substrates 49A toform the channels 48 as shown in FIG. 2A. The substrates 49A can bemetal sheets coated with the desiccant. The channels 48 in FIG. 2A havea triangular cross-section. However, it should be understood that thechannels 48 in other embodiment may have different shapes. The channels48 of the desiccant wheel 40 include surface one of more surfaces 52coated with desiccant. Air flows contacts and flows across the surfaces52 as it flows through the channels 48 of the desiccant wheel.

FIG. 2B is a cross-section of a channel 48 of the desiccant wheel 40 asindicated in FIG. 2A, according to an embodiment. As shown in FIG. 2B, acoating 54 of the desiccant composition is applied to one or moresurfaces 52 of the desiccant wheel 50. For example, the coating 54 isapplied to the frame 50 of the desiccant wheel 40 (e.g., the metalplates/substrates that form the channels 48 of the frame 50). In anembodiment, the surface(s) 52 are metal surface(s) of the frame 50 ofthe desiccant wheel 40. The coating 54 can be formed by applying (e.g.,coating, spraying, or the like) an application mixture that includes thedesiccant composition and solvent to the surface(s) 52 of the desiccantwheel 40. The application mixture then dries on the surface(s) 52 toform the coating 52. In an embodiment, the application mixture containsless than 10 wt % of the solvent. In an embodiment, the solvent is anon-aromatic solvent. In an embodiment, the solvent is a non-aromaticalcohol or water.

The binder is used to adhere the MOF desiccant to the surface(s) 52 ofthe frame 50 of the desiccant wheel 40. The binder also provides thecoating 52 with cohesion to the surface(s) 52 of the frame 50. Thebinder configured to provide cohesion capable of withstanding thecontinuous vibration that occurs due to the rotation of the desiccantwheel 40. The coating 52 also has temperature and humidity stabilityover the temperatures and humidities that can occur within the AHU 10.

In an embodiment, the binder in the desiccant composition is polyvinylbutyral. For example, polyvinyl butyral binder has found to have anadvantageous compatibility with the relatively narrow RH band MOFdesiccant of the desiccant wheel 40. For example, polyvinyl butyralbinder was found to provide good cohesion while having a low impact onthe water uptake of the relatively narrow RH band MOF desiccant. In anembodiment, the coating 52 contains 10 wt % or less of binder. Coatingscontaining more than 10 wt % of binder were found to cause the coating52 to either flake off from the frame 50 and/or have a significantlyimpact the water uptake capacity of the MOF desiccant. In an embodiment,a coating containing AL-MIL-68-Mes MOF and 10% of less of polyvinylbutyral binder was found to have good water uptake and adherence.

In an embodiment, the desiccant composition includes less than 8.0 wt %of the binder. In an embodiment, the desiccant composition includes 7.8wt % or less of the binder. In an embodiment, the desiccant compositionincludes 5.5 wt % of the binder. In an embodiment, the desiccantcomposition includes at or about 2.7 wt % of the binder.

The MOF desiccant is a desiccant that has an adsorption isotherm and adesorption isotherm that each have an “S” shape. This type of “S” shapedisotherm is referred to as a Type V isotherm. Accordingly, a desiccantwith “S” shaped absorption and desorption isotherms can be referred toas Type V desiccant. A desiccant has an uptake capacity that describeshow much water the desiccant can adsorb. Uptake capacity varies with thehumidity of the air flowing to/along the desiccant. The adsorptionisotherm illustrates the relationship between uptake capacity andrelative humidity when dry MOF desiccant is adsorbing water from air.The desorption isotherm illustrates the relationship between uptakecapacity and relative humidity when water containing MOF desiccant isdesorbing water. In particular, the s-shaped isotherms of the MOFdesiccant each include an steep middle section.

An absorption inflection point is the point in the adsorption isothermat which the water uptake capacity increases and transitions from thesteep middle section. For example, the point in the adsorption isothermat which the water uptake capacity is no longer exponentiallyincreasing. The desorption inflection point is the transition point inthe desorption isotherm at which the water uptake capacity decreases andtransitions out of the steep middle section. For example, the point inthe desorption isotherm at which the water uptake capacity is no longerexponentially decreasing.

Desiccants have an absorption-desorption operating band that is therelative humidity range defined by an upper end point at which thedesiccant is configured to operate to adsorb moisture and a lower endpoint at which the desiccant is configured to desorb moisture into air.Type V desiccants can have an majority absorption-desorption operatingband that is the humidity range defined by the steep middle sections ofthe adsorption isotherm and the desorption isotherm. The majorityabsorption-desorption operating band is the humidity range defined bythe end of the exponential decrease in the desorption isotherm and theend of the exponential increase in the adsorption isotherm (e.g., thehumidity range that has a lower end point of the desorption inflectionpoint and an upper end point of the adsorption inflection point). Themajority absorption-desorption operating band includes an uptakecapacity change of at least 50% of the maximum uptake capacity of thedesiccant. In an embodiment, the desiccant wheel 40 contains an MOFdesiccant with an majority absorption-desorption operating band in whichthe uptake capacity changes by at least 60% of the maximum uptakecapacity of the MOF desiccant

The MOF desiccant in the desiccant wheel 40 has an adsorption isothermand desorption isotherm that operate in relatively narrowerabsorption-desorption relative humidity operating band. In anembodiment, the MOF desiccant has a majority operating band of 25%relative humidity or less. For example, the MOF desiccant has an uptakecapacity change of at least 50% of its maximum uptake capacity within25% relative humidity or less. In another embodiment, the MOF desiccanthas an operating band of 20% relatively humidity or less. In anembodiment, the MOF desiccant has an exponential operating band of 15%relative humidity or less.

The adsorption isotherm has a steep middle section. In an embodiment,the adsorption isotherm section has at least a portion with a slope ofat least 80 degrees relative to horizontal. In an embodiment, the steepmiddle section has at least a portion with a slope of at least 85degrees relative to horizontal. In an embodiment, the portion of theadsorption isotherm is along a range of at least 2% of relativehumidity.

The MOF desiccant can have an adsorption inflection point that occursbetween 50% and 80% relative humidity. In an embodiment, MOF desiccanthas an adsorption inflection point that occurs between 65% and 75%relative humidity.

The MOF desiccant can have a desorption inflection point that occursbetween 40% and 60% relative humidity. In an embodiment, the MOFdesiccant has a desorption inflection point that is between 40% and 55%relative humidity.

The MOF desiccant in desiccant wheel 40 is a type V MOF desiccant withan absorption-desorption operating band having one or more of theproperties described above (e.g., a narrower majorityabsorption-desorption operating band, an adsorption inflection point,desorption inflection point location, a minimum change over theoperating band). In an embodiment, the MOF desiccant is a type V MOFdesiccant with an absorption-desorption operating band having at leastthe narrower majority relative humidity operating band described above.In an embodiment, the MOF desiccant is a type V MOF desiccant with anmajority absorption-desorption operating band having at least thenarrower majority relative humidity operating band and the uptakecapacity change within its majority operating band as described above.In an embodiment, the MOF desiccant is a type V MOF desiccant with anmajority absorption-desorption operating band having at least thenarrower majority relative humidity operating band, the adsorptioninflection point, and a desorption inflection point as described above.

The MOF desiccant in desiccant wheel 40 can be, for example but notlimited to, AL-MIL-68-Mes MOF and/or CAU-3-BDC (AL) MOF. AL-MIL-68-MesMOF and CAU-3-BDC (AL) MOF are provided as examples. It would beappreciated that the MOF desiccant can be other type V MOFs that haveabsorption-desorption properties as described herein.

FIG. 3 is a graph illustrating adsorption and desorption forAL-MIL-68-Mes MOF (referred “AL-68 MOF”). The graph in FIG. 3 shows anadsorption isotherm 202 and a desorption isotherm 212 for the AL-68 MOF.The adsorption isotherm 202 shows the water uptake capacity of the AL-68MOF at different relative humilities. The AL-68 MOF is a type Vdesiccant that has an S shaped adsorption isotherm 202 and an S shapeddesorption isotherm 212.

The water uptake capacity of AL-68 MOF was tested at a series ofincreasing relative humilities. For example, air at a specific relativehumidity is supplied through/to a sample of AL-68 MOF powder and thenthe mass of the sample of AL-68 MOF powder (with its adsorbed water) isused to determine the amount of water adsorbed by the powder. Thistesting data was plotted on a graph of uptake vs. relative humidity(e.g., the graph in FIG. 3 ) and a curved trend line was fit to the datapoints to generate the adsorption isotherm 202. After reaching themaximum water uptake capacity of the sample AL-68 MOF, the testingprocess was conducted in reverse at a series of decreasing relativehumidities to determine the desorption isotherm 212. The water uptakecapacity of the AL-68 MOF was measured at 25° C. and standard pressure(1 atm).

Each of the s-shaped isotherms 202, 212 includes an steep middle section204, 214. The adsorption isotherm 202 includes an steep middle section204 and an adsorption inflection point 206. The steep middle section 204is middle portion of the S-shape that is disposed between the two tailsections of the S-shape. The steep middle section 204 is the portion inwhich the adsorption isotherm 202 exponentially increases (e.g., theportion in which the water uptake of the AL-68 MOF increasesexponentially. The absorption inflection point 206 is the point in theadsorption isotherm 202 at which the adsorption isotherm 202 is nolonger increasing exponentially. For example, the inflection point 206is the point at which the adsorption isotherm stops increasingexponentially and begins to level off.

The desorption isotherm 212 includes an steep middle section 214 and adesorption inflection point 216. The steep middle section 214 is middleportion of the S-shape that is disposed between the two tail sections ofthe S-shape. The steep middle section 204 is the portion in which theuptake of the desorption isotherm 212 exponentially decreases (e.g., theportion in which the water uptake of the AL-68 MOF decreasesexponentially). The desorption inflection point 216 is the point in theadsorption isotherm 202 at which the desorption isotherm 212 is nolonger decreasing exponentially. For example, the desorption inflectionpoint 216 is the point at which the desorption isotherm 212 stopsdecreasing exponentially.

As shown in FIG. 3 , the adsorption inflection point 206 occurs at orabout 55% relative humidity, at which the AL-68 MOF has an uptakecapacity of 330 mg water per 1 g of the MOF. The desorption inflectionpoint 216 occurs at or about 43% relative humidity, at which the AL-68MOF has an uptake capacity of 67 mg water per gram of the AL-68 MOF. TheAL-68 MOF has an exponential absorption-desorption operating band 220 of12% relative humidity (e.g., 55%−43%). The AL-68 MOF has a maximumuptake capacity 222 of 375 mg water per gram of the AL-68 MOF (e.g., 375[mg water]/[1 g MOF]. The uptake capacity of the AL-68 MOF changes by˜70% of its maximum uptake capacity 222 across its majority operatingband (e.g., [330 mg/g−67 mg/g]/[375 mg/g]=70%). The uptake capacity ofthe AL-68 MOF decreasing by ˜80% across its smaller majorityabsorption-desorption operating band. This can be advantageous as itallows for air with a higher humidity (e.g., the air F₁ in FIG. 1 ) tobe used to provide significant regeneration of the desiccant.

FIG. 4 is a graph illustrating adsorption and desorption for a CAU-3-BDC(AL) MOF (herein referred to as “second MOF desiccant”). The graph inFIG. 4 shows an adsorption isotherm 302 and a desorption isotherm 312for the second MOF desiccant. The adsorption isotherm 302 shows thewater uptake capacity of the second MOF desiccant at different relativehumilities. The second MOF desiccant is a type V desiccant that has an Sshaped adsorption isotherm 302 and an S shaped desorption isotherm 312.The adsorption isotherm 302 and a desorption isotherm 312 weredetermined for the second MOF desiccant in the same manner as discussedabove for the MIL-68-Mes MOF.

Each of the s-shaped isotherms 302, 312 have the same general structureas described above for s-shaped isotherms 202, 212 in FIG. 3 . Forexample, the adsorption isotherm 302 includes an steep middle section304 and an adsorption inflection point 306, and the desorption isotherm312 includes an steep middle section 314 and a desorption inflectionpoint 316.

As shown in FIG. 4 , the adsorption inflection point 306 occurs at orabout 67% relative humidity, at which the second desiccant MOF has anuptake capacity of 550 mg water per 1 g of the MOF. The desorptioninflection point 316 occurs at or about 53% relative humidity, at whichthe second desiccant MOF has an uptake capacity of 158 mg water per gramof the MOF. The second desiccant MOF has a majorityabsorption-desorption operating band of 14% relative humidity (e.g.,67%−54%). The second desiccant MOF has a maximum uptake capacity 322 of633 mg water per gram of the MOF (e.g., 633 [mg water]/[1 g MOF]. Theuptake capacity of the second desiccant MOF changes by ˜62% of itsmaximum uptake capacity across its majority absorption-desorptionoperating band (e.g., [550 mg/g−158 mg/g]/[633 mg/g]=62%). The uptakecapacity of the MIL-68-Mes MOF decreases by ˜72% across its smallermajority absorption-desorption operating band.

In conventional dehumidifying AHUs, the temperature and relativehumidity of the inlet air was not sufficient for regenerating theconventional desiccant. The conventional AHU would include a heaterupstream of the first end 46A of the desiccant wheel 40 so that heatedinlet air capable of sufficiently regenerating the conventionaldesiccant flows through the first end 46A. As shown in FIG. 1 , the AHU10 in an embodiment does not include a heater between the air inlet 16and the first end 46A of the desiccant wheel 40, and does not heat thereturn air or the ambient air provided to the first end 46A of thedesiccant wheel 40.

The MOF desiccant in desiccant wheel 40 advantageous allows for coolingand dehumidifying air without needing to provide heated air (e.g.,providing a heat element, a heating heat exchanger, and the like) toregenerate the desiccant. This advantageously allows for the AHU 10 tohave a reduced latent load. The MOF desiccant also has a higherefficiency than previous desiccants which advantageously allows for lessdesiccant to be used and for the desiccant wheel to be lighter.

Aspects:

Any of Aspects 1-11 may be combined with any of aspects 12-17.

Aspect 1. A dehumidifying air handling unit for an HVACR system,comprising: a housing including an air inlet and an air dischargeoutlet, a main airflow path extending through the housing from the airinlet to the air discharge outlet; a desiccant wheel including a firstend disposed in the main airflow path, a second end disposed in the mainairflow path downstream of the first end, and a metal organic framework(“MOF”) desiccant, the desiccant wheel rotatable to move the MOFdesiccant between the first end and the second end of the desiccantwheel, the MOF desiccant having an majority absorption-desorptionoperating band of 25% relative humidity or less; and a cooling heatexchanger disposed in the main flow path downstream of the first end ofthe desiccant wheel and upstream of the second end of the desiccantwheel.Aspect 2. The dehumidifying air handling unit of Aspect 1, wherein theMOF desiccant positioned at the second end of the desiccant wheel isconfigured to adsorb water from air flowing through the main airflowpath, and the MOF desiccant positioned at the first end of the desiccantwheel configured to desorb water into the air flowing through the mainairflow path.Aspect 3. The dehumidifying air handling unit of either one of Aspects 1or 2, wherein the air flowing through the main airflow path flows alongthe first end of the desiccant wheel.Aspect 4. The dehumidifying air handling unit of any one of Aspects 1-3,wherein the MOF desiccant positioned at the first end is configured todesorb the water into the air having a temperature of 40° or less.Aspect 5. The dehumidifying air handling unit of any one of Aspects 1-4,wherein the AHU does not have a heater disposed in the main airflow pathdownstream of the air inlet and upstream of the first end of thedesiccant wheel.Aspect 6. The dehumidifying air handling unit of any one of Aspects 1-5,wherein the MOF desiccant has an adsorption isotherm with an adsorptioninflection point that occurs between 50% and 80% relative humidity.Aspect 7. The dehumidifying air handling unit of any one of Aspects 1-6,wherein the MOF desiccant has a desorption isotherm with a desorptioninflection point that occurs between 40% and 60% relative humidity.Aspect 8. The dehumidifying air handling unit of any one of Aspects 1-7,wherein the MOF desiccant has a maximum uptake capacity, and uptakecapacity of the MOF desiccant changes within the majorityabsorption-desorption operating band of the MOF desiccant by at least50% of the maximum uptake capacity of the MOF desiccant.Aspect 9. The dehumidifying air handling unit of any one of Aspects 1-8,wherein the MOF desiccant has an “S” shaped adsorption isotherm.Aspect 10. The dehumidifying air handling unit of any one of Aspects1-9, wherein the desiccant wheel includes a coating on a surface of thedesiccant wheel, the coating including the MOF desiccant and a binder,the coating containing 10 wt % or less of the binder.Aspect 11. The dehumidifying air handling unit of any one of Aspects1-10, further comprising: a motor disposed in the housing, the motorconfigured to rotate the desiccant wheel.Aspect 12. A desiccant wheel for an air exchange unit of an HVACRsystem, the desiccant wheel configured to be rotated within the airexchange unit, the desiccant wheel comprising: a first end and a secondend; a metal organic framework (“MOF”) desiccant disposed on a surfaceof the desiccant wheel, the rotation of the desiccant wheel configuredto move a position of the surface between the first end and the secondend, the MOF desiccant having an majority absorption-desorptionoperating band of 25% relative humidity or less.Aspect 13. The desiccant wheel of Aspect 12, wherein the MOF desiccanthas an adsorption isotherm with an adsorption inflection point thatoccurs between 50% and 80% relative humidity.Aspect 14. The desiccant wheel of either one of Aspects 12 or 13,wherein the MOF desiccant has a desorption isotherm with a desorptioninflection point that occurs between 40% and 60% relative humidity.Aspect 15. The desiccant wheel of any one of Aspects 12-14, wherein theMOF desiccant has a maximum uptake capacity, and uptake capacity of theMOF desiccant changes within the majority absorption-desorptionoperating band of the MOF desiccant by at least 50% of the maximumuptake capacity of the MOF desiccant.Aspect 16. The desiccant wheel of any one of Aspects 12-15, wherein theMOF desiccant has an “S” shaped adsorption isotherm.Aspect 17. The desiccant wheel of any one of Aspects 12-16, comprising:a frame including the surface; and a coating disposed on the surface ofthe frame, the coating including the MOF desiccant and a binder, and thecoating containing 10 wt % or less of the binder.

The examples disclosed in this application are to be considered in allrespects as illustrative and not limitative. The scope of the inventionis indicated by the appended claims rather than by the foregoingdescription; and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A dehumidifying air handling unit for a heating,ventilation, air conditioning, and refrigeration system, comprising: ahousing including an air inlet and an air discharge outlet, a mainairflow path extending through the housing from the air inlet to the airdischarge outlet; a desiccant wheel including a first end disposed inthe main airflow path, a second end disposed in the main airflow pathdownstream of the first end, and a metal organic framework (“MOF”)desiccant, the desiccant wheel rotatable to move the MOF desiccantbetween the first end and the second end of the desiccant wheel, the MOFdesiccant having a majority absorption-desorption operating band of 25%relative humidity or less; and a cooling heat exchanger disposed in themain flow path downstream of the first end of the desiccant wheel andupstream of the second end of the desiccant wheel.
 2. The dehumidifyingair handling unit of claim 1, wherein the MOF desiccant positioned atthe second end of the desiccant wheel is configured to adsorb water fromair flowing through the main airflow path, and the MOF desiccantpositioned at the first end of the desiccant wheel is configured todesorb water into the air flowing through the main airflow path.
 3. Thedehumidifying air handling unit of claim 2, wherein the air flowingthrough the main airflow path flows along the first end of the desiccantwheel.
 4. The dehumidifying air handling unit of claim 2, wherein theMOF desiccant positioned at the first end is configured to desorb thewater into the air having a temperature of 40° or less.
 5. Thedehumidifying air handling unit of claim 1, wherein the air handlingunit does not have a heater disposed in the main airflow path downstreamof the air inlet and upstream of the first end of the desiccant wheel.6. The dehumidifying air handling unit of claim 1, wherein the MOFdesiccant has an adsorption isotherm with an adsorption inflection pointthat occurs between 50% and 80% relative humidity.
 7. The dehumidifyingair handling unit of claim 1, wherein the MOF desiccant has a desorptionisotherm with a desorption inflection point that occurs between 40% and60% relative humidity.
 8. The dehumidifying air handling unit of claim1, wherein the MOF desiccant has a maximum uptake capacity, and uptakecapacity of the MOF desiccant changes within the majorityabsorption-desorption operating band of the MOF desiccant by at least50% of the maximum uptake capacity of the MOF desiccant.
 9. Thedehumidifying air handling unit of claim 1, wherein the MOF desiccanthas an “S” shaped adsorption isotherm.
 10. The dehumidifying airhandling unit of claim 1, wherein the desiccant wheel includes a coatingon a surface of the desiccant wheel, the coating including the MOFdesiccant and a binder, the coating containing 10 wt % or less of thebinder.
 11. The dehumidifying air handling unit of claim 1, furthercomprising: a motor disposed in the housing, the motor configured torotate the desiccant wheel.
 12. A desiccant wheel for an air handlingunit of a heating, ventilation, air conditioning, and refrigerationsystem, the desiccant wheel configured to be rotated within the airhandling unit, the desiccant wheel comprising: a first end and a secondend; and a metal organic framework (“MOF”) desiccant disposed on asurface of the desiccant wheel, the rotation of the desiccant wheelconfigured to move a position of the surface between the first end andthe second end, the MOF desiccant having a majorityabsorption-desorption operating band of 25% relative humidity or less.13. The desiccant wheel of claim 12, wherein the MOF desiccant has anadsorption isotherm with an adsorption inflection point that occursbetween 50% and 80% relative humidity.
 14. The desiccant wheel of claim12, wherein the MOF desiccant has a desorption isotherm with adesorption inflection point that occurs between 40% and 60% relativehumidity.
 15. The desiccant wheel of claim 12, wherein the MOF desiccanthas a maximum uptake capacity, and uptake capacity of the MOF desiccantchanges within the majority absorption-desorption operating band of theMOF desiccant by at least 50% of the maximum uptake capacity of the MOFdesiccant.
 16. The desiccant wheel of claim 12, wherein the MOFdesiccant has an “S” shaped adsorption isotherm.
 17. The desiccant wheelof claim 12, comprising: a frame including the surface; and a coatingdisposed on the surface of the frame, the coating including the MOFdesiccant and a binder, and the coating containing 10 wt % or less ofthe binder.